A PIN diode is essentially a variable resistor that converts optical energy to electrical current. Both the resistance and the responsivity of the PIN are parametric to the bias conditions of the diode. Due to the nature of the way that a PIN diode operates, there is usually a need for PIN bias schemes to ensure that the PIN operates in an appropriate fashion. Especially in optical communication systems, a PIN diode at the receiver side of the optical communication system will benefit from a bias scheme. Most optical communication systems that employ a PIN diode also utilize a transimpedance amplifier (TIA) to help amplify the electrical signal output by the PIN diode.
Traditional PIN bias schemes utilize an external supply voltage for biasing the photodiode. High performance photodiodes often require a high supply voltage that is often greater than the supply voltage of the TIA. The use of an external photodiode bias voltage leads to a high frequency ground path through a decoupling capacitor that is not the same to the TIA's connection to the ground. These different ground paths can greatly degrade an optical receiver's high speed performance.